Metabolic diseases and disorders are widely recognized as serious health problems for developed countries, having reached epidemic levels in the United States. According to recent studies on obesity, for example, more than 50% of the U.S. population is considered overweight, with more than 25% diagnosed as clinically obese and at considerable risk for heart disease, type 2 diabetes and certain cancers. This epidemic presents a significant burden on the health care system as projected obesity treatment costs of more than $70 billion annually are expected in the U.S. alone. Strategies for treating obesity include reduction of food intake and enhancing the expenditure of energy.
Neuropeptide Y (NPY), a 36 amino acid peptide neurotransmitter, is a member of the pancreatic polypeptide class of neurotransmitters/neurohormones which has been shown to be present in both the periphery and central nervous system. NPY is one of the most potent orexogenic agents known and has been shown to play a major role in the regulation of food intake in animals, including humans.
Six neuropeptide Y receptors (NPY), the Y1-, Y2-, Y3-, Y4, and Y5- and Y6-subtypes, have been cloned, which belong to the rhodopsin-like G-protein-coupled 7-transmembrane spanning receptors (GPCR). The NPY Y2 receptor (Y2R) is a 381 amino-acid receptor which inhibits the activation of adenyl cyclase via Gi while displaying low homology with other known NPY receptors. There is a high degree of conservation between rat and human Y2 receptors with 98% amino acid identity.
The Y2R receptor is widely distributed within the central nervous system in both rodents and humans. In the hypothalamus, Y2 mRNA is localized in the arcuate nucleus, preoptic nucleus, and dorsomedial nucleus. In the human brain, Y2R is the predominant Y receptor subtype. Within the arcuate nucleus, over 80% of the NPY neurons co-express Y2R mRNA. Application of a Y2-selective agonist has been shown to reduce the release of NPY from hypothalamic slices in vitro, whereas the Y2 non-peptide antagonist BIIE0246 increases NPY release. These findings support the role of Y2R as a presynaptic autoreceptor that regulates the NPY release and hence may be involved in the regulation of feeding. (Kaga, T. et al., Peptides 22: 501-506 (2001) and King P J et al., Eur J Pharmacol 396: R1-3 (2000)).
Peptide YY3-36 (PYY3-36) is a 34 amino acid linear peptide having neuropeptide Y2 (NPY2R) agonist activity. It has been demonstrated that Intra-arcuate (IC) or Intra-peritoneal (IP) injection of PYY3-36 reduced feeding in rats and, as a chronic treatment, reduced body weight gain. Intra-venous (IV) infusion (0.8 pmol/kg/min) for 90 min of PYY3-36 reduced food intake in obese and normal human subjects over 24 hours. These finding suggest that the PYY system may be a therapeutic target for the treatment of obesity. (Batterham R L et al., Nature 418: 650-654 (2002); Batterham R L et al., New Engl J Med 349: 941-948 (2003)). Further, a Cys2-(D)Cys27-cyclized version of PYY, in which residues 5-24 were replaced by a methylene-chain of 5 to 8 carbons in length, showed activation of the intestinal PYY receptor, as evidenced by reduced current across voltage-clamped mucosal preparations of rat jejunum. (Krstenansky, et al. in Peptides, Proceedings of the Twelfth American Peptide Symposium. J. Smith and J. Rivier Editors, ESCOM. Leiden Page 136-137).
In addition, recent data have shown that Roux-enY gastric bypass patients have an early and exaggerated increase in PYY levels that may be partly responsible for the early glycemic control and long term weight maintenance demonstrating the importance of this peptide in the pathogenesis of metabolic diseases. Other known actions of PYY include: reduced gastric emptying and delayed gastrointestinal transit that is responsible for improved postprandial glycemic control. Indices of hyperglycaemia such as HbA1C and fructosamine show a dose-dependent reduction after peripheral administration of PYY3-36 in animal models of type 2 diabetes. Thus, these results indicate that PYY3-36, or pharmaceutically related agonists, may offer a long term therapeutic approach to glycemic and weight control. (Korner et al., J Clin Endocrinol Metabol 90: 359-365 (2005); Chan J L et al., Obesity 14: 194-198 (2006); Stratis C et al., Obes Surg 16: 752-758 (2006); Borg C M et al., Br J Surg 93: 210-215 (2006); and Pittner R A et al., Int J Obes 28: 963-971 (2004)).
A need exists, however, for novel engineered analogs of PYY having lower molecular weight, while possessing equal or better potency and selectivity against Y1, Y4 and Y5 receptors, pharmacokinetic properties and pharmacological properties.